20 research outputs found
The role of symmetric vibrational modes in the dehoherence of correlation-driven charge migration
Due to the electron correlation, a fast removal of an electron from a
molecule may create a coherent superposition of cationic states and in this way
initiate pure electronic dynamics in which the hole-charge left by ionization
migrates throughout the system on an ultrashort time scale. The coupling to the
nuclear motion introduces a decoherence that eventually traps the charge and a
crucial question in the field of attochemistry is how long the electronic
coherence lasts and which nuclear degrees of freedom are mostly responsible for
the decoherence. Here, we report full-dimensional quantum calculations of the
concerted electron-nuclear dynamics following outer-valence ionization of
propynamide, which reveal that the pure electronic coherences last only 2-3 fs
before being destroyed by the nuclear motion. Our analysis shows that the
normal modes that are mostly responsible for the fast electronic decoherence
are the symmetric in-plane modes. All other modes have little or no effect on
the charge migration. This information can be useful to guide the development
of reduced dimensionality models for larger systems or the search of molecules
with long coherence times
PAH under XUV excitation: an ultrafast XUV- photochemistry experiment for astrophysics
International audienceUnderstanding processes induced by XUV excitation of Polycyclic Aromatic Hydrocarbons (PAHs) is at the heart of molecular astrophysics, which aims at understanding molecular evolution in interstellar media. We used ultrashort XUV pulses to produce highly excited PAHs cations. The photo-induced dynamics is probed using a pump-probe XUV-IR spectroscopy. By studying PAH from small (naphthalene) to large (hexabenzocoronene) PAHs, we show that the dynamic is governed by the large density of states, in which many-body quantum effects are dominant
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XUV excitation followed by ultrafast non-adiabatic relaxation in PAH molecules as a femto-astrochemistry experiment
Highly excited molecular species are at play in the chemistry of interstellar media and are involved in the creation of radiation damage in a biological tissue. Recently developed ultrashort extreme ultraviolet light sources offer the high excitation energies and ultrafast time-resolution required for probing the dynamics of highly excited molecular states on femtosecond (fs) (1 fs=10−15s) and even attosecond (as) (1 as=10−18 s) timescales. Here we show that polycyclic aromatic hydrocarbons (PAHs) undergo ultrafast relaxation on a few tens of femtoseconds timescales, involving an interplay between the electronic and vibrational degrees of freedom. Our work reveals a general property of excited radical PAHs that can help to elucidate the assignment of diffuse interstellar absorption bands in astrochemistry, and provides a benchmark for the manner in which coupled electronic and nuclear dynamics determines reaction pathways in large molecules following extreme ultraviolet excitation
Ultrafast vibrational relaxation dynamics in XUV-excited Polycyclic Aromatic Hydrocarbon molecules
Interstellar matter and star formatio
Ultrafast dynamics of correlation bands following XUV molecular photoionization
Interstellar matter and star formatio
Balanced Schnyder woods for planar triangulations: an experimental study with applications to graph drawing and graph separators
In this work we consider balanced Schnyder woods for planar graphs, which are
Schnyder woods where the number of incoming edges of each color at each vertex
is balanced as much as possible. We provide a simple linear-time heuristic
leading to obtain well balanced Schnyder woods in practice. As test
applications we consider two important algorithmic problems: the computation of
Schnyder drawings and of small cycle separators. While not being able to
provide theoretical guarantees, our experimental results (on a wide collection
of planar graphs) suggest that the use of balanced Schnyder woods leads to an
improvement of the quality of the layout of Schnyder drawings, and provides an
efficient tool for computing short and balanced cycle separators.Comment: Appears in the Proceedings of the 27th International Symposium on
Graph Drawing and Network Visualization (GD 2019
XUV excitation followed by ultrafast non-adiabatic relaxation in PAH molecules as a femto-astrochemistry experiment
15Highly excited molecular species are at play in the chemistry of interstellar media and are involved in the creation of radiation damage in a biological tissue. Recently developed ultrashort extreme ultraviolet light sources offer the high excitation energies and ultrafast time-resolution required for probing the dynamics of highly excited molecular states on femtosecond (fs) (1 fs=10−15s) and even attosecond (as) (1 as=10−18 s) timescales. Here we show that polycyclic aromatic hydrocarbons (PAHs) undergo ultrafast relaxation on a few tens of femtoseconds timescales, involving an interplay between the electronic and vibrational degrees of freedom. Our work reveals a general property of excited radical PAHs that can help to elucidate the assignment of diffuse interstellar absorption bands in astrochemistry, and provides a benchmark for the manner in which coupled electronic and nuclear dynamics determines reaction pathways in large molecules following extreme ultraviolet excitation.openopenMarciniak, A.*; Despré, V.; Barillot, T.; Rouzée, A.; Galbraith, M.C.E.; Klei, J.; Yang, C.-H.; Smeenk, C.T.L.; Loriot, V.; Reddy, S. Nagaprasad; Tielens, A.G.G.M.; Mahapatra, S.; Kuleff, A.I.; Vrakking, M.J.J.; Lépine, F.Marciniak, A.; Despré, V.; Barillot, T.; Rouzée, A.; Galbraith, M. C. E.; Klei, J.; Yang, C. -H.; Smeenk, C. T. L.; Loriot, V.; Reddy, S. Nagaprasad; Tielens, A. G. G. M.; Mahapatra, S.; Kuleff, A. I.; Vrakking, M. J. J.; Lépine, F
Decoherence and revival in attosecond charge migration driven by non-adiabatic dynamics
Attosecond charge migration is a periodic evolution of the charge density at specific sites of a molecule on a timescale defined by the energy intervals between the electronic states involved. Here we report the observation of charge migration in neutral silane (SiH4) in 690 as, its decoherence within 15 fs and its revival after 40-50 fs, using X-ray attosecond transient-absorption spectroscopy. We observe the migration of charge as pairs of quantum beats with a characteristic spectral phase in the transient spectrum, in agreement with theory. The decay and revival of the degree of electronic coherence is found to be a result of both adiabatic and non-adiabatic dynamics in the populated Rydberg and valence states. The experimental results are supported by fully quantum-mechanical ab initio calculations that include both electronic and nuclear dynamics, which additionally support the experimental evidence that conical intersections can mediate the transfer of electronic coherence from an initial superposition state to another one involving a different lower-lying state.ISSN:1745-2473ISSN:1745-248
PAH under XUV excitation: an ultrafast XUV-photochemistry experiment for astrophysics
Understanding processes induced by XUV excitation of Polycyclic Aromatic Hydrocarbons (PAHs) is at the heart of molecular astrophysics, which aims at understanding molecular evolution in interstellar media. We used ultrashort XUV pulses to produce highly excited PAHs cations. The photo-induced dynamics is probed using a pump-probe XUV-IR spectroscopy. By studying PAH from small (naphthalene) to large (hexabenzocoronene) PAHs, we show that the dynamic is governed by the large density of states, in which many-body quantum effects are dominant